Oh Fuck brother, I've been there. I've stuttered my whole life but one of my worst periods was at your age. Went from being mostly fluent to not being able to say anything. Found a really good speech therapist that made a world of difference. He had one trick that really helped me so I'm going to pass it along here: just stop. Like you I always knew which word I was going you stutter on, sometimes sentences in advance, and being a stubborn bastard I'd just plow head first into them. Turning red and running out of breath just trying to force my way through each block with brute strength. It never worked but that's what I thought I needed to do. He taught me to stop and turn my mind's eye inward and wait for the block to loosen. And with me, it usually does go away after about 10 seconds or so. The weirdest part to me is I could say other words, just not that one I knew I was going to block on. I used to have a little speech for those times. I'd get stuck on a word, catch myself trying to push through the block, stop, take a deep breath, relax, and say to whoever I was speaking to "sorry, I'm stuck on that word. You'll have to give me a sec." Usually by the time I was done saying that the block would have loosened I could continue with what I was saying in the first place. I'm 40 now and my stutter is very mild. Still can't say my name to save my ass and I will walk a mile just so I don't have to try and call someone but, all in all, it's a sweet life. Like those LGBT adds, I just want to tell you that it does get better.